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Woodside bridges to have their secrets revealed

 

An issue with the potential to disrupt Woodside's village character is once again before the Town Council: What should be done about three small bridges, each at least 100 years old, to make sure they are safe and sound?

The council directed staff on March 11 to prepare a proposal to have engineers examine the vulnerabilities of these single-span bridges on Kings Mountain Road (over Union Creek), Mountain Home Road (over Bear Gulch Creek) and Portola Road (over Alimbique Creek).

The California Department of Transportation in 2009 declared the bridges "functionally obsolete" and possibly structurally deficient, according to a town staff report. While federal money is available to pay for 89 percent of the cost of upgrading or replacing them, that money would come with an aesthetic compromise: much wider roadways, in keeping with federal bridge standards.

The council is looking for alternatives, and may vote on an engineering-analysis contract at its March 25 meeting.

The council first looked at this issue in November 2012. It's getting back to the council only now because "Caltrans spent a heckuva lot of time not answering our questions," Town Engineer Paul Nagengast told the council.

The traffic lanes of the current bridges are 18 feet to 20 feet wide. Simply replacing them would widen the lanes to at least 28 feet. Adding the necessary pedestrian and equestrian crossings, either separately or combined as one bridge, would bring the total width to about 40 feet.

The bridges are arguably not equipped for modern two-way traffic; vehicles are heavier and larger than they were 100 years ago, and there are many more of them.

Untouched, the bridges may have another 20 years before Caltrans might consider a ban on heavy traffic such as cement trucks, possibly even fire trucks and garbage trucks, professional engineer Steven L. Mellon, of Sacramento-based Quincy Engineering, told the council in November 2012.

An informed decision based on an analysis of the three bridges would run a total of about $159,000. While the council was hardly enthusiastic about that level of spending, and while no agency is forcing the town to replace its bridges, the cost of doing nothing could be much higher were one of them to collapse.

The bridge analysis would include core samples, hydraulic evaluation, X-rays to locate concrete reinforcing bars, a study of scouring issues around abutments, a set of plans for the bridge as it was built, and possible next steps, Mr. Mellon said.

It's unclear whether that $159,000 would be eligible for federal reimbursement.

Replacements would run about $2 million each for the Kings Mountain and Mountain Home road bridges, and about $1 million for the Portola Road bridge a simple span over a metal culvert. The study of the Portola Road bridge will include a look at realigning the approaches to make crossing less daunting to drivers.

If the analyses turn up structural issues, the council will be looking for ways to use federal money without compromising the rural character of the bridges.

The Kings Mountain and Mountain Home bridges are eligible to be designated as historically significant, which might be advantageous at some point. The required environmental analysis would run between $60,000 and $150,000 per bridge, Mr. Mellon said. "Environmental processes for a federally funded project, it gets pretty expensive," he said.

Fix, not replace

Mayor Dave Burow asked about the chances of using federal money to upgrade the bridges without making them much wider. "It's a tough battle," Mr. Mellon said. "It's not very common, but it has been done before."

Councilman Peter Mason, an architect, responded. "It is possible to fix stuff. It's done all the time," he said. In a summation later, he noted that the council's goal "is to fix the bridges, not replace them."

Resident Steve Lubin, citing the visual and historical importance of the bridges at their current widths, urged the council to use town funds.

Thalia Lubin, who is married to Steve Lubin and is a member of the town's History Committee, called the Kings Mountain and Mountain Home bridges "character defining" and suggested a fundraising campaign.

Councilman Tom Shanahan reiterated his longstanding objections to using federal funds for local purposes and wondered aloud why Woodside could not be like Rome, which is home to bridges that are thousands of years old.

Councilman Dave Tanner, a general contractor, said that longevity depends on the concrete's chemistry.

Mike Cook, the lab manager at Graniterock concrete manufacturing in Watsonville, told the Almanac that the quality of the materials in ancient concrete made it very dense and nonporous compared to modern concrete. "The lack of porosity means that environmental pollutants and water have a very difficult time getting into the concrete and as a consequence the degradation of the concrete is slowed significantly," Mr. Cook said in an email.

Keith Severson, Graniterock's marketing communications manager, agreed with Mr. Tanner in that the chemistry of the interior aggregate can be reactive and create subsurface problems, as can corroding reinforcing bars. A lot depends on the expertise that went into the original construction, he said.

Comments

Like this comment
Posted by Robert Cronin
a resident of Menlo Park: The Willows
on Mar 21, 2014 at 6:17 pm

I don't understand how Woodside's "rural character" is so fragile that it depends on a trio of old bridges for its preservation.


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